shetlands need as much space as any other horse, but the pasture shouldnt have much grass or they will get laminitis. Other than that all a shettie needs is some good quality hay. Grain will make them horrendously fat. They evolved to survive on nothing but extremely poor grass so any supplementary feeding is usually too much. They will be quite happy on just grass most of the time, with hay if it snows and a little when it gets very cold. You can also feed a little chaff (a handful is enough) with a broad base vitamin and mineral supplement every day to keep a good mineral balance because of the poor quality of the grass they have to have to avoid laminitis. (or provide a mineral lick) You can feed increased amounts of hay if the pony loses weight (unlikely in a shetland but could happen) or feed some dengie HiFi. Grain is a bit of a no-no for shetlands because they cant handle it easily.

heya, we have 2 shetland ponies, and they are on about 4 acres at mo with a 13.1 pony. the grass is slightly low around here, but we feed them.
We feed them 1 scoop cool mix, 1 handful chaff 1 scoop sugar beet, and hay (sometimes) and they are fine. there really fat, they onli need about 1 acres each ?

natural way if your shetlands are really fat then you are feeding them way too much (have to say you are feeding them the same amount i feed my two 14.2hh ponies and MORE than my 13.2hh gets)
You could probably cut right down until you are just feeding them the chaff and they would still be fat.
Remember Obese ponies get laminitis, generally fat ponies = bad for all sorts of reasons - and shetlands are particularly prone to laminitis. In their natural habitat they eat nothing but really terrible quality grass, any grass you have will be like gourmet food for them however bad you think it is, its probably still sufficient with just a bit of seed hay to supplement.
Lou

I've got two shetlands and during the winter they can "free graze" off of the hay feeder and come in at night and get a 1/2 a flake of hay and a couple of handfuls of sweetfeed. During the summer we rotate them around from a pasture with lots of grass to one that's got less grass in it.